Refractory



Patented June 7, 1932 UNITED STATES GEORGE A. SOPER, JR., OF' .ALBANY NEW YORK REFBACTORY Application led October 29, 1928. Serial No. 815,779.

My invention relates to refractories and particularly to bricks or blocks to be used in furnaces or the like and which are provided with a facing or veneer capable of resisting much higher temperatures than the backing or body of the block.

Where extremely high temperatures are to be encountered in a furnace, it is usual to employ in the facing of the walls, arches, etc.,

) bricks made entirely of silicon carbide, otherwise known as carborundum. Bricks or blocks of this material are extremely expensive, and cost, at the present time, some-v tures, silicon carbide is an excellent conductoi: of heat, its heat conductivity far exceeding that of ordinaryfire clay. In addition to covering the exposed face of the brick with silicon carbide I propose to utilize this great heat conductivity for thepurpose of cooling or conducting the heat away from the furnace wall.

One of the'objects of my invention is to provide a brick or block having a refractory facing or veneer of silicon carbide and which will have all of the advantages of a block made entirely of silicon carbide but which o may be manufactured at a very much less cost. More specically, it is an object of my invention to provide a brick or block, the major -pNrtion of which will be formed of high grade fire clay but which will have, on the side or sides directly exposed'to the heat, a

facing or veneer of silicon carbide substantially welded or fused thereon. Another object of my invention is to provide a brick or block which will be particularly adapted for use in so-called air-cooled walls and where- -structures described below and illustrated in 2, are formed, into which portions of the by heat may be readily conducted from the front to the back of the Wall.

With these objects in view my invention includes the method of procedure and the the accompanying drawing in which- Fig. l is a perspective View of a block embodying features of my invention; 4

Fig. 2 is a vertical section of the block in the plane 2-2 of Fig. 1; v

Fig. 3 is a section of Fig. 1 in the 'plane 3 3; and f' Fig. ais a section similar to Fig. 3 but of a modied form of the block.

In proceeding to manufacture a refractory having a carborundum facing thereon it is quite important that only the highest grade of fire clay, such for example as Pennsylvania iiint clay be used in the molding of the block. Using a lire clay of this character the block, 1, is formed in the ordinary way with the exception that upon the side to which the facing is to be applied, undercut grooves or recesses,

carborundum facing will enter and interlock. 76 In practice, these recesses may be cut rather easily by means of a knife while the clay is plastic, or they may be molded therein by using small chips or -blocks of wood in the bottom of the mold and around which the plastic fire clay is molded. After molding it is not necessary to remove the chips or blocks because they will be destroyed when the block is burned. Where it is desired to apply a facing to a block in which no openings have beenl provided in the molding thereof or before burning, undercut recesses or grooves may be cut therein with comparative ease by means of an air chisel.

After the block is formed as above described, it is burned in the usual way thusA forming, with the exception of the grooves or-recesses therein, a re brick or block of the ordinary type. After burning, it is desirable to remove from the surface to which the facing is -to be applied the skin which is formed thereon during the burning process, and to roughen the block by means of a sand blast, air chisel or otherwise.

Referring to Figs. 3 and 4, 1 represents the |00 vfm body portion of the block which is of high grade ire clay, 2` represents reentrant or undercutgrooves or recesses in the face of the block, and 3 represents the roughened portions of the surface from which the skin has been removed between the undercuts. Portions of the sides adjoining the side to which the facing is to be applied are also roughened as shown at 4. i

The facing of silicon carbide is then prepared as a plastic mass having about the consistency of stiff putty and as follows: Granulated silicon carbide is intermiXed with what I choose to call a temporaryair-drying binder, a substance which will form a permanent binder when burned, and with water, if necessary, to form a plastic mass. By the term temporary air-drying binder7 I mean a material such as a glue, a resin, a starch or other adhesive which will harden when exposed to the air and which will be comparatively easily burned. By a substance which will form a permanent binder when burned, I mean a clay which when fused will form a glass-like matriX in which the grains of silicon carbide will be embedded and secured together. In the selection of such a permanent binder it is quite essential that a clay having a wide range of vitrification be used and that it be very nely divided or comminuted. Silicon carbide grain with from 10% to 20% of such a clay is miXed together with the temporary air-drying binder, and water if necessary, to form a plastic mass having about the consistency of stiff putty. This plastic mass is applied to the block to form a veneer, 5, of the desired thickness over the face which has been especially prepared therefor. In practice, I find that a thickness of one-half an inch is generally sufficient although it is to be understood that practically any thickness may be applied. Before applying the silicon carbide, the block should be thoroughly cleaned by washing, and the application 'should be made while the block is still wet.

' Where the block is burned in this condition the results are not entirely satisfactory because the ire seems to enter the joint between the block and the facing causing a separation thereof and a warping of the face. To eliminate this warping and separation, I prepare a mixture of silicon carbide grain, temporary air-drying binder and permanent binder of about the consistency of whipping cream and paint over the joint between the facing and the brick as shown at 6. It is desirable to make this coating of paint about ,15 in thickness and to apply one or more coats until this thickness is attained. While not necessary, it is at least desirable in order to preserve the uniform rectangularity of the block that the entire block be painted over as shown at 7.

The block is then thoroughly dried and is first burned at a comparatively low temperature for a sufficient length of time to oXidiZe the temporary binder. Thereafter the temperature of the kiln is raised and the block is burned for a sufiicient length of time to effect a formation of the permanent binder. To obtain the best results it is essential that the clay used in forming the temporary binder have such a wide range of vitrication as to form a glass matrix at a temperature which will not cause deformation of that portion of the block which is formed of ordinary fire clay. In burning the blocks with the facing thereon, no stress should be put upon the facing, and the block should be supported in thekiln in such a way that this result will be obtained.

l/Vhere it is desired to utilize the high heat conductivity of the silicon carbide for the purpose of cooling the wall, -the efficiency of the cooling may be greatly increased by connecting the front and back of the block with one or more cores of silicon carbide, such as shown at 8 in Figs. 2 and 3. Such cores may be slightly conical in form, as shown in Fig. 3, and serve, in part, to bind thefacing and block together. By using such a form of construction, heat will be readily conducted through the core from the front to the back of the wall where it may be absorbed by forcing air across the backs of the blocks.

While there is a tendency. for the face and block to separate when burned if the joint between the two is not covered with silicon carbide, I nd that by covering the joint, as above described, this difficulty is entirely eliminated, and the facing seems to be drawn very tightly against the block so that test specimens, when fractured, indicated that the facing and the block are substantially integral.

I have described my invention in its preferred embodiment only, but it is to be understood that the words which I have used are words of description rather than of limitation, and that changes within the purview of the appended claims may be made without departing from the true scope and spirit of my invention in its broader aspects.

For example, while bricks of chrome, mullite or other highly refractory substances are frequently used in lieu of carborundum, in describing and claiming my invention I have mentioned only the latter. I wish it to be clearly understood, however, that Y invention contemplates the use, as desclrilbed and claimed in respect of silicon carbide, of other materials having refractory characteristics similar thereto, and that the term silicon carbide in the claims shall mean and include such materials.

1. A refractory block comprising a body portion of fire clay having a facing of silicon carbide substantially integral therewith; said facing being of substantial thickness over one face of the block but comparatively thin on the faces adjacent the first mentioned face,

2. A refractory block comprising a body portion of fire clay and a veneer of silicon carbide substantially integral therewith; said veneer being continuous throughout and of substantial thickness over one face of said block but otherwise comparatively thin. 3. A refractory block having a facing of silicon carbide on one side thereof and a core of silicon carbide extending through said block from the facing to the side opposite the facing.

4. A block of the character described comprising a body portion of refractory material having a relatively low heat conductivity, a facing of refractory material having a relatively high heat conductivity and a core of material having a relatively high heat conductivity extending from the facing to the side of said block opposite the facin GEORGE A. SOPE JR. 

